Corridors and Reserve Design

Connectivity

Connectivity can be defined as the relative degree to which individual animals, and genes, can move across a landscape. Natural landscapes have an inherent degree of connectivity to which species have adapted over time. Habitat alteration practices of humans greatly reduce that connectivity for the majority of wildlife species. In many cases, a narrow corridor is all that remains to allow for the movement of wildlife.

Biosphere Reserve Design

The immediate challenge is to design reserves for wildlife that can sustain wildlife populations as human populations continue to increase outside the reserves. The basic design consists of a core reserve where human activities are limited and the maintenance of wildlife habitat and biodiversity are the primary goals. Dr. Reed Noss, with the Wildlands Project, has refined this concept. Surrounding the core are buffer zones where increasing amounts of human impacts are allowed, but which can also support many species of wildlife. Outside of the buffer zones, land use is primarily human-oriented and only very human-tolerant wildlife species are found. Wherever possible, core reserves are connected by secure corridor habitat which is also surrounded by buffer zones.

Connected Reserves

In designing reserves, we are trying to conserve as much of the natural connectivity as possible in the face of human population growth and human developments. A basic assumption of this project is that an interconnected network of reserves will be more effective in maintaining populations of carnivores than would smaller, more isolated reserves. A second assumption of this project is that a reserve design that maintains large carnivores will also maintain prey populations, smaller carnivores, and the majority of native plants and animals. This is known as the umbrella species concept.

The landscape we are focusing on encompasses the Rocky Mountains from the Canadian Border to the southern edge of the Greater Yellowstone Ecosystem. This area is often referred to as the Northern Rockies unless you live in Canada where these are your Southern Rockies!

Northern Rockies Reserve Network

An initial conceptual diagram of a reserve design for this immediate area was something like this. Imagine that the three large core areas approximate the Northern Continental Divide Ecosystem [NCDE] the Greater Yellowstone Ecosystem [GYE] and the Salmon-Selway Ecosystem [SSE].

The larger vision for North America extends this idea further north as embodied in the Yukon-to-Yellowstone concept and the World Wildlife Fund's Large Carnivore Conservation project, and extends the idea all across the continent as embodied in The Wildlands Project concept.

A first stage map of a reserve design for the Northern Rockies, based on effective habitat for three wildlife species (elk, grizzly bear, and mountain lion (created with the support of American Wildlands), looks like this:

[GIS habitat-based reserve]

Potential Regional Network of Wildlife Habitat in the U.S. Northern Rockies.

Richard Walker and Lance Craighead, supported by American Wildlands, developed this GIS analysis of core reserve and corridor habitat in the Northern Rockies of Montana, Idaho, and Wyoming. This map is based upon habitat effectiveness models for three umbrella species: elk, mountain lion, and grizzly bear. Data were derived from Montana Gap Analysis vegetation layers and from several sources of road density information. A detailed description of this process was presented at the 1997 ESRI Users Conference (Paper 116).

A closer look at the Bozeman area shows corridors connecting the Gallatin, Madison, Tobacco Root, Bridger, Absaroka, Gravelly, and Elkhorn Ranges.

Core areas of suitable habitat (magenta) are connected by routes that represent the shortest path through good habitat with the least risk in terms of human activities and disturbance.

In the prospective corridors, warmer colors offer the best potential path while cooler colors represent lower habitat effectiveness.

Corridor Analysis

With the support of American Wildlands "corridor analysis" project scientists now at CERI completed the first phase of a multidisciplinary and cooperative approach to measure and describe the connectivity that remains in the Northern Rockies landscape. The analysis process identified critical areas where connectivity is constrained for certain species - either because of human activities or because of natural landscape and biotic features. Such features are bottlenecks in the larger corridors. Once identified, natural bottlenecks can be managed to retain their inherent connectivity. Human-caused bottlenecks can only be altered again to restore the connectivity they have lost.

The results of corridor mapping with the support of American Wildlands are the foundation for this Northern Rockies Reserve Matrix which is being refined with further GIS analysis by CERI. As a part of this Reserve Design work the Craighead Environmental Research Institute cooperated in a project with the Montana Department of Fish, Wildlife, and Parks to follow dispersing juvenile mountain lions when they leave their mother's home range in the Beartooth Game Range as a partial test of the corridor mapping results.

The results of two years of field work are displayed on CERI's Dispersal Study pages.